Thermoplastic polymers in the molten state are often filtered to remove impurities, such as solids and/or gels, before they are passed to a mold cavity or through a die plate. Examples of polymer filtering devices are shown in U.S. Pat. No. 4,701,118, U.S. Pat. No. 5,004,414, and U.S. Pat. No. 6,641,728.
The filter portion of these devices typically includes a foraminous supporting plate and a plurality of filters resembling sticks or candles. The filters themselves are composed of tubular support structures with one or more filter media in the form of a sleeve wrapped around the tubular support structures.
Both the foraminous supporting plates and the tubular support structures available in the market today, however, suffer from a number of disadvantages. For example, the design of the tubular support structures is not very efficient for filtering or for replacement. Moreover, the foraminous supporting plates and the tubular support structures are susceptible to cracking and breakage under normal use.
Thus, there is a need in the art for improved foraminous supporting plates and tubular support structures for filtering polymer melts.
The present invention addresses this need as well as others, which will become apparent from the following description and the appended claims.